Flexible mandrel



Dec. 5, 1933. M EATON 1,937,644

FLEXIBLE MANDREL Filed March 21, 1951 3 Sheets-Sheet l ww-nssscs 17 vINVENTOR 771M541 Z Wxw/Mw Dec. 5, 1933. G EATON 1,937,644

FLEXI BLE MANDREL Filed March 21, 1951 s Sheets- Sheet 2 INVENTOR G. M.EATON FLEXI BLE MANDREL 3 Sheets-Sheet 3 Filed March 21 1931 2%AAA\\\\\\\\\\\ INVENTOR mmxw/MAW Dec. 5, 1933.

VITNESSES 77 WW Patented Dec. 5, 1933 r 1,937,644 FLEXIBLE MANDR LGeorge M. Eaton, Ben Avon, Pa., a'ssignor to Spang, Chalfant & 00.,Inc., Pittsburgh, Pa., a corporation of Pennsylvania Application March21, 1931. Serial 1%.524535 ,7 Claims. (01. 1o '107 My invention relatesto the supporting of tubing against deflection or distortion whensubjected to exteriorly applied forces, and is particularly applicableto the holding of tubing during the cutting 5 of threads on its surface,or while performing other heavy cutting operations on it.

Much time and effort have been expendedin attempting to cut threads onthe exterior of pipe by a hobbing operation, in which, and in certain(10 other thread cutting processes, very heavy cuts are taken at oneside only of the pipe. In practice it has been found that. the pressureexerted by the cutting tool against the pipe in taking such cuts issuflicient to deflect or distort the pipe to such extent that when thecutting operation is completed and the pipe returns to its relaxed shapethe threads are so distorted and inaccurate that the pipe cannot beused. I

An attempt has been made to overcome this difficulty by inserting asolid cylindrical mandrel in the pipe to support it during the hobbingoperation. However, inasmuch as the inner surface of commercial pipe andsimilar tubular members are ordinarily not accurately cylindrical, acylindrical mandrel causes the pipe to be deflected out of its normalrelaxed shape when it is inserted. Hence, after threads have been out onthe surface of the deflected pipe and the mandrel removed, the pipereturns to its originalrelaxed shape, thus destroying the accuracy ofthe threads.

Mandrels having independent supporting elements actuated by fluidpressure or similar means have been tried, but have also been found tobe inadequate to support the pipe in its relaxed shape.

fluid pressure mandrels tend to force the pipe to cylindrical shape, orto permit it to be deflected towards cylindrical shape when acted uponby external force. well known principle that tubular objects tend toassumeoylindrical shape when subjected to internal fluid pressure. Forexample, if the tube to be supported by a fluid pressure operatedmandrel is somewhat elliptical in shape, the mandrel tends to distort itto cylindrical shape. Or, if the mandrel is not sufliciently powerful todo-so, a heavy external force applied along the major axis of theellipse will distort the tube to a shape more nearly cylindrical. thecross sectional area of the tube is increased and the volume of thespace occupied by the fluid is correspondingly increased. This occursboth in cases in which the fluid isapplied'directlyto the tube and incase a mandrel having fluid actuated supporting member is utilized. Ifthe operating Just as in 'lhe case of solid cylindrical mandrels;

This is in accordance with the In so changing shape fluid is confined bynon-resilient means, such i ncrease in volume'reduces the workingpressure the mandrel and permits further distortion of the tube. I

It is an object of this invention to provide a 6.0 method of accuratelycutting threads on pipe wherein the pipe isheld firmly and rigidly inits normal relaxed shape during the thread cutting operation. r

Another object of my invention is to provide 65. a, mandrel forsupporting. a tubular body that conforms accurately to the interiorshape of the tubular'body and that holds it rigidly in its nor-: malrelaxed position.

. A further object is to provide an expans'ible mandrel that iseconomical to. manufacture and that is rugged and easily manipulated.

In accordance with my invention, 'Iprovide a mandrel having a pluralityof work-engaging members, each member being providedwith two independentcontact areas. Means are provided for moving the members tobring all of.the contact areas into engagement with the innersurface of thetubularbody to be supported. The means for moving the supportingmembersfinclude a8!) wedge member disposed to exert equal forces on thesupporting members;- and .to set up frictional forces between themembers and the tubular body," and between itself and the members tolockthem in position.

' I I The foregoing and other objects of the inven tion will becomemore" fullyiapparent as a better understanding of. the invention is hadupon studying the specific structures'd'escribed in this speciflcationand shown in theaccom'pan'ying' draw- 9Q ing's, in which Fig."1 is aview inend elevation of an expansible" mandrel, embodying my invention,disposed within a-tube; Fig. 2 is a view in; section of the mandrelshown in Fig; 1 taken on the plane indicated by theline II-' II therein;

Fig. 3 is a plan view showing in conventional man'- ner a thread hobbingmachine in which is mounted a pipe supported by'the mandrel embodying myinvention; Fig. 4 n view showing one element of my flexibleman'dreldisposed withina 10.0"

.tube; Fig. 5 is a viewjsimilar-to Fig. 4 showing means foradaptingthemandrel to tubes o1 vari-f' ous diameters; Fig. 61s a view similar toFig. 4 showing, on a reduced scale,a niodiflcation of'm'y.

invention; Fig. '7 is a'view in section similar to Fig. Zof anothermodification of my-invention;-

and Fig. 8 is-a view, similar to Fig. 7, of the modi flcation of myinvention shown in Fig. 6 taken on the plane representedby the line Thethread hobbing machine shown in Fig. 1 1- 3 is of well known'type withwhich my flexible mandrel is ordinarily utilized. In general the hobbingmachine comprises a base 1 upon which is rotatably' mounted a hollowhead stock or chuck 2 having clutch jaws for receiving a tubular bodyhob 4 may be rotated by any suitable means such' as a motor 7 mounted onthe carriage and connected to the hob bya transmission mechanism 8.During the cutting operation the carriage 5 is moved longitudinally ofthe base 1, at proper speed to form threads of the desired pitch ontherotating pipe 3, by means of a lead screw 9 driven in synchronism withthe pipe by a gear train 10 that connects it directly to the rotatinghead stock 2.

' To'insure that the force exerted by the hob 4 in performing thecuttingoperation willnotdistortthepipe 3, the end of the pipe isreenforced, in accordance with my invention, by an expansible mandrel 15disposed within the pipe and held-in engagement with it in 'such'mannerthat the pipe is firmlyand rigidly supported in its normal relaxedposition. Themandrel 15 ordinarily may be placed in position manuallyand operated to engage the interior of thepipe 3 by suitable'operatingmechanism actuated by a T-handle' 16. The pipe 3 is shown in thedrawings as being of truly circular cross section for simplicity ofillustration, but it will be understood that commerciallyaccepted pipeis not made truly cylindrical but-varies from such shape to anappreciable extent. Fora better understanding of the construction ofthe-mandrel 15 that is adapted to support the pipe in itsnatural shape,reference may be had to Fig. 4 in which one supporting element 1'7 only"is shown in its retracted position within a tubular object 3; As shown,the supportingelement 1'7 comprises a plurality; of rigid members18,-each of which is provided with two contact areas 19 for with therigid members 18., the entire element 17 havingbeen cut fromasingleplate of suitable 1 metal by a cutting torch or other cuttingdevice! ii To expand the supporting e1ementf1'7 and movethe'ccntactareas 19' into engagement with the inner surface of thetube3, I provide a conical wedge member 22 that engages a seat 23 attheinner, edgeofreach rigid member 18.

' If We assume'that-theielement l'l is'initially out of contactwith thepipeS as shown in Fig". 4, it

may be readily-appreciated that'when the conical member "22 is. advancedaxiallybetween the seats 23 0f the rigid members 18 it causes them tomove outwardly untilone contact area 19 of one member 18 engages theinner surface of the, pipe. In-' asmuch as there-is no resistancetomovement .of

the other two-members 18' they will continue to move outwardlyuntil atleast one contact area of each has also engaged-the pipe 3.'Uponfurther' axial movement of the cone22 the rigid nembers 18" willpivot about theirinitial'points of contact with the pipe3"'andwill-slide on the interior of the p pe and on the exterior of thecone 2' until position is reached in which both of the contact areas 19on each of the members 18 engage the pipe 3.

In bringing the supporting element 1'7 into engagement with the interiorof the pipe 3 at all six of thecontact areas only sufficient force needbe exerted to overcome the tension in the springs 21, which is small,and to overcome the slight friction between the various members. as oneor more of the contact areas 19 has not yet engaged the tubular object3, the forces within the device are negligible, inasmuch as the mem-.bers not in full engagement with the pipe are free to move withoutsubstantial resistance until they do engage thepipe at both contactareas.

However, as soon as all of the contact areas have engaged the pipe 3,further movement of the cone 22 will set up substantial radial forceswithin the supporting element 1'7 that will oppose external radialforces that may be applied to the pipe during thread cutting or othermachining operations and will set up frictional resistance to opposechange of shape of the element. In the preferred practical embodiment ofmy As long invention, shown in Figs. 1 and 2, I utilize two N in Fig. 2,and will stand in stablemanner while being manipulated toexpand it intoengagementwith the tube. To distribute the forces exerted by theelements 17 and 27'about the tube 3, the

contact areas of the two elements are disposed in radial planes atangles of 30 to each other in such manner that twelve'substantiallyequally spaced contact areas are provided.- The angular relation betweenthe elements 1'7 and- 2? is maintained by a pin 28 securely held in theplate 27 by a nut 29 and extending through a hole 39 in the plate 17. Topermit limited relative motion between the plates 1'7 and 2'7, the hole,30 is made somewhat larger than the pin 28 to provide adequate clearancespace.

The flexible element 2'7 may be actuated by a cone 32 similar to thecone 22in the element 1'7 but extending into the element2'7 in theopposite direction. As shown in Fig.2, the elements 1'7 and 2'7 may beexpanded simultaneously'by moving the cones 22 and 32 toward each other.

This may be conveniently accomplished by an operating shaft 34 providedwith left and right hand threaded portions which cooperate withcomplementary internal threads in the cones 2 2 and 32, respectively.The shaft 3 is connected to the operating handle 16 by means of which itmay 4 toward or away from. each other.

I To hold the elements 1'7 and 2'7 inspaced rela tion, the members 18 ofeach are provided on their adjacent faces with spacing members 35 1 thatbearagainst each other. At the other sides of l the members 18 there areprovided similar members 36 which serve to thicken theelements andprovide relatively wide tapered faces 23 and 33 for, engaging the cones22 and 32, respectively.

To prevent the cones from turningwith theoperating shaft 34, keyways 3'7and 47 are provided in'the seats 23 and 33 of' the elements for co-'operating with keys 38' and 18 on thecones 22 and 32, respectively; Thekey 48' and the key- 7 be rotated to move the cones22 and 32 tion.However, incrder 'to'permit some-relative.

angular motion between. the elements 17 and," 2'7, the keyway 3'? ismade somewhat larger than the key 38 in'the same manner and for the sameIn operation the mandrel 15 is placed within the tube '3 andthe'h'andlelfi'is actuated to turn the shaft 34 in the clockwise.direction, as viewed from the'right end of Fig; 2. 1 This'causes thecones 22 and 32 to approach each other and to force the rigid members 18of the elements 17 and 27 outwardly. Comparatively small forces 'will berequired to turn the shaft 34 at first and the rigid members 18 willshift about slightly as they move outwardly until all of the twelvecontact areas 19 engage the inner surface of the tube 3'. After themandrel 15 has thus adjusteditself to conform to the interiorconfiguration of the tube 3, further rotation of the shaft 34 will buildup forces that act radially outward upon the tube 3 through'all of thecontact areas 19 to support it inits normal or relaxed position. Toeffectively support the pipe 3 against distortion, the cones 22 and 32are advanced to such position that the forces exerted upon the tube 3 bythe members 18 are as large as can safely be ap- 25 plied without undulyexpanding the tube. Inasmuch as the forces exerted by the cones 22 and32 upon the rigid members 18 are substantially equal, the forces appliedto the tube .3 .by the contact areas 19 are also substantially equal toeach other regardless of the configuration of the interior of the tube3. Further, during the time that the supporting forces are being builtup there is practically no relative motion between the various parts ofthe mandrel, and, as the radial forces increase, tangential frictionalresistances are set up tending to lock the elements 17 and 27 securelyin position. I

As a result of the radial forces between the H contact areas 19 and thetube, frictional resist-' ances are established therebetween whichoppose relative circumferential motion of the tube and the supportingelements 17 and 27. .Relative motion between the elements 17 and. 27also is opposed by frictional resistance between the spacing members35'which-results from the opposing longitudinal force exerted by thecones 22 and 32. To assist in locking the mandrel, the surfaces of thecones 22 and 32 are disposed at such angles to their axes as to providefor irreversible action between the cones and the seats of the members18. Hence, after the cones havebeen moved within the elements to pointsin which the desired forces'are set up, theyare held from retracting bythe frictional forces betweenv them and the seats 23 and 33. Likewisefrictional resistances to motion are setup between the threads in thecones 22 and 32, and the threads of the shaft 34.

It is apparent that. afterthe mandrel 15 has been. expanded to apply therequired supporting forces to the tube 3, the frictional resistances tomotion that are set up between itsvariousparts and between it and thetube 3 are of such nature as to prevent relative motion between theelements of thedevice when the tube issubjected to externally appliedforces. In order .to change the shape of the mandrel thus locked itwould be necessary to rock or rotate one or more of the rigid members l8relative tothe other members. Such relative rotationof the memberswouldre sult in relative sliding motion between the members and thecones or the pipe. But. as has been explained, such relative slidingmotion is effec- Q tively resisted by the large frictional forces setupbetween'the members and the various surfaces which-they engage. j

.After the mandrel has been expanded to its final position and locked byfrictional resistance, it functions substantially as would a solidmandrel that had been carefully fitted to conform to the irregularitiesof the interiors'of the pipe. However, inasmuch as the mandrel engagesthe interior of the pipe at twelve separate and distinct positions,there. is a slight tendency to deflect the pipe from its relaxed shapetowards'a shape in the nature of a polygon having twelve sides; That is,the pipe is. deflected outwardly; to a slight extent, at each of thepoints to which pressure is applied by the twelve contact areas of themandrel. This deflection is. so'slight, however, that it has noappreciable effect uponthe accuracy of'the threads cut on the pipe whilethus supported. In view of the negligibleeifect of this slightdistortion it may be-saidithat, for.

-vide a mandrel for supporting pipe against the distorting effect ofheavy forces applied .to. its

exterior while cutting threads on it. Y

With the mandrel thus locked in position with:

in the tube the exterior of the tubemay be threaded or otherwise workedupon without dan ger of springing or deflecting it and impairing theaccuracy of. the work. -Afterthe threading or other operation has beenperformed the. man-v drel 15 maybe retracted for withdrawal from thetube by turning the operating handle 16 counter-clockwise, whichoperation causes the cones 22 and 32 to move away from each other. Asthe cones are separated the working forces within the mandrel l5 vare-'gradua11yreducedto zero and'as the retracting operation progresses therigid members 18 are drawn inwardly to their" inactive positions by thesprings 21. The mandrel may then be withdrawn leaving the pipe in itsoriginal shape with accurately cut threads of true pitch diameter on itssurface.

To prevent damage to the mandrel 15 in the event that the operating.handle 16 is actuated when the mandrel is not in .a pipe. that it isadaptedto support, the cones 22 and 32 are made of such length that theywill engage each other at the mid-plane of the mandrel before theelements 1'7 and 27 can be expanded to stress the springs 21 beyondtheir elastic limits. Incidentally, the stresses within the spring 21during normal use of the mandrel are quite low ihasmuch as thesupportingforces are-transmitted directly through the rigid members 18.v

In the event that it is desirable to utilize one mandrel for supportingpipes of different internal dimensions, adapters or' lugs 39 may beapplied to;

the rigid members 18, as shown in Fig. 5. In this view the lugs 39 areshown attached by bolts 40 tonne members 18 at each contact position 19.A set of lugs 39 may be provided for adapting the i mandrel 15 to eachsize-of pipe with which itgis to be utilized. 7 r u Under someconditions'it may be desirable to support the pipe at the ,position inwhich it is gripped by the clutch jaws of the chuck 2 as well;

as at the position upon whichz th'e cutting tool operates. If suchsupport is provided the clutch jawsmay be disposed to engagethe pipenearthe to rigidly grip the pipe without danger of distorting it.Apparatus for accomplishing the result is provided by the modificationof my invene tion shown in Fig. 7. In this modificationtwo completemandrel structures or units, ,eachsimilar to that shown in Figs. 1 and2, are operatively connected to a common operating mechanism. As shown,one mandrel unit a isdisposed near the end of the pipe 3 'to support itagainst distor tion by forces exerted by the cutting tool 4a. To preventdistortion of the pipe bythe chuck2 another mandrel unit .4500 isdisposed, somewhat farther within the pipe 3 at the position engaged bythe clutch: jaws 2a of the rotating head stock.

The two mandrel units 1511 and a are spaced or positioned by a hollowcompression member or nipple 47a. At the ends of the nipple 47a. are

. operating cones 420;, corresponding to'the cone threads of arelativelylong operating shaft 34a that passes through the nipple 47a. As shown,

the cones 52a are at the ends of the apparatus and it is apparent thatwhen they are moved toward each other by the shaft 3% they not onlyoperate the particular element which they engage but also force'theother elements of the mandrel units on the cones 42a. Consequently, whenthe shaft 34a is actuated by the handle 16a to tighten I the apparatuswithin the pipe 3 all of the four having cones 42b at their ends, areprovided for) vided with'small rollers or wheels 56b mounted areasengage the inner surface'of the pipe.

elements expand Lmtil all twenty-four contact AS the mandrel elementsare forced von the cones 42a the entire apparatus is shortened somewhatand the mandrel units 15a and 45a are moved toward'e'ach other. Suchmotion can readily take place during the adjusting period when there is'f very little frictional resistance to motion between the contact areasand the pipe; After all the contact areas engage the pipe and pressureis exerted by turning the shaft 34a farther there will be some slighttendency to move the mandrel units toward each other. However, thistendency is readily taken care of by deflection of the resil-. ientelements of themandrel. I 4

- In the event that it is desirable to support the pipe at more than twopositions apparatus constructed in accordance with the modification of'my invention shown in Figs. '6 and 8 maybe utilized. In thismodification a plurality of mandrel units 1512,45!) and b,respectively,are all mountedon'a long 'operating'shaft 342); At the endsof the shaft 342) the usual right. and left threads are provided forengaging complementary threads in end cones 5219p Spacing nipples 47b,

separating the mandrel units.

As mandrel apparatus of this type may be made quite long, meansareprovided for permitting. some of the units to move longitudinally ofthe pipe when the endcones-52b are drawn toward each other. To this end,all of the mandrel units" except the one at the endof the pipe are proateach contact position and disposed in radial longitudinal planes of "thepipe 3,-as shown in r Fig. 6.

From the "foregoing description of my. tube supporting mandrel andexplanation of the manner in which. it operates, it is selfeevident thatI have provided rugged and effective apparatus for firmly supporting 'atubular object in-its normal or relaxed position to resistdistortionfrom externally applied forces. I Y 1 Although I have shown only a fewspecific embodiments of my invention and have described them in detailto adequately disclose the inven- .tion, it will be apparent tothoseskilled-in the art that many modifications may be made in the details ofthe mandrels, as in the types ofspring elements utilized and'in thegeneral configurae tion and number of the rigid members,withoutdeparting from the spirit and scope of my invention as defined in theappended claims.

I claim: I;

1. In a mandrel for providing, internal support to a tubular object ofapproximately circu lar shape in cross section, a plurality ofsupporting elements disposed in pairs in spaced transverse planes of theobject to be supported, each of said elements comprising a plurality ofrigid members provided'with a plurality of contact areas forengagingtheinner surfaceof the rigid members of each supporting elementoutwardly, the cones for-actuating each pair of elements being disposedto move toward each other, rigid means disposed to space the elements ofeach pair, compression members disposedxbe-r tween the conesat adjacentsides of successive tubular object, a cone disposed to actuate the gpairsto space the-pairs, and means for actuating ing equally all of theelements'of the mandrel.

with rollers disposed in radial transverse planes of the tubular objectfor .engaging'the inner sur face-thereof, a cone disposed to actuate therigid members of "each supporting element outwardly, the cones foractuating each pair of elements being disposed to move toward eachother, rigid'-- means disposed to space the elementsof each pair,compression members-disposed between the cones at adjacent sides ofsuccessive pairs to space the pairs, and means "for actuating the conesat the ends of the mandrelv to move them I toward each other and inv so.doing move the cones in each pairtoward each other for ex panding"equally all of the' elements ofthe mandrel. E

3.-Means for radially supporting a hollow work-piece, comprisingaplurality of engaging members arranged in a circle andmountedfor.

radial-movementand for tilting movement substantially in the plane ofthe circle, each of said" members having two independent contact areasspaced apart from each other, and means'for ex erting substantiallyradial pressure" upon said members in a direction towards saidwork-piece,

whereby each of said members iscaused to seat with both of its surfacesagainstsaid work-piece.

4:. Means for radially supporting a hollow work-piece, comprising aplurality of" engaging members arranged in a circle and mounted iorfradial movement and for tiltingimovement sub spaced apart from eachother, an axially movable wedge member Contacting said engaging membersfor moving them in a substantially radial direction, whereby each ofsaid members is caused to seat with both of its surfaces against saidwork-piece. v

5. A mandrel for interiorly supporting a hollow work-piece, comprising aflat plate having portions thereof removed to produce a group of membersarranged in a circle and having outerferentially of the circle, each ofsaid bases having two independent contact areas spaced apart from eachother, and their apexes directed toward the center of the circle andintegral resilient portions connecting said engaging portions, and

means for exerting substantially radial pressure upon the apexesof'saidengaging-portions.

7. A mandrel for interiorly supporting a hollow work-piece, comprising aplate having por tions thereof removed to produce a group of sub--sta'ntially triangular engaging; portions arranged in a circle withtheir bases disposed circumferentially of the circle, each of said baseshaving two independent contact areas spaced apartfrom each other, thesides of said triangles being con-' cave to produce spaces between saidportions and the apexes of said portions being directed toward thecenter of the circle, and U-shaped integral resilient portions disposedin said spaces and connecting said engaging portions, and means forexerting substantially radial pressure upon the apexes of said engagingportions.

. GEORGE M. EATON.

